Having a similar problem, but the 12V is fine. Press start button and nothing happens, but 12 volt is fine when tested. Even replaced 12 volt twice in the last year. It will start immediately with a jump and will continue to restart for a month or more, then the system goes dead again. I am thinking it is either a relay switch sticking (or not making contact) or a problem with the computer. It seems like something between the battery and the start button or ignition system is failing. We had also been getting the "System shutting down to save battery" message usually a couple of days before the problem occurs. The problem throws no codes, so the dealer is unable to diagnose the problem. Dealer had the car for 3 or 4 days and as usual was unable to duplicate the problem. Love the car, but can not live with unreliability and will probably be trading it in soon.
